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Natural sciences

Grade 9

Energy, forces and machines

Module 22

Power

Performance (effort/work) is important, but the SPEED at which it is performed is also important.

Activity:

Explaining the concept power and calculating it

[lo 2.3; lo 2.4]

POWER = WORK / TIME

We measure this in J/s, or Watt (W)

1J per second provides 1 Watt of power

  • The term Watt is derived from the name of James Watt, who was responsible for improvements to the steam engine.
  • The electricity in your home is measured in kilowatt-hour (kWh) .
  • One kilowatt-hour is the energy output of a 1 kW appliance in one hour.
  • The longer such an appliance is operated, the more energy is used. A 2 kW heater that is operated for three hours will therefore use 6 kW energy.
  • Complete: …… kW per hour x …… hour = 6 kW.
  • The cost of a kWh varies but comes to approximately R0,35 in the Western Cape.

Assignment:

Measure your own power capacity

  • Identify a stairway in the school and measure the height of a step.
  • Multiply this by the number of steps.
  • Determine your weight.
  • Run up the stairs and take your time in seconds.

Complete the following table:

Aspect Measurement
Step height
Mass
Weight
Work performed: F x s
Time

QUESTIONS

1. What was your power?

2. Explain the following:

a) Kilowatt

b) Kilowatt-hour

3. Find out what the power rating of the average car (your educator's car, for instance) is.

4. Would you be prepared to push your educator's car all the way home? Why not?

5. Why would it be easier for the car engine to do this, even though you might have enough time and help from your friends?

6. Calculate the cost of operating a 3 000 W heater for a month (July) for 4 hours per day at a tariff of R0,35 per kWh.

Assessment of the CALCULATION of POWER CAPACITY

Were you able to apply knowledge and do the calculations?

[LO 2.3; LO 2.4]

Activity:

Doing research on power and performing relevant calculations

[lo 1.1; lo 1.2; lo 2.2; lo 2.4]

Find out what 1 kWh of electricity costs in your municipal area.

Suppose you use the following appliances during the day:

  • Computer for 2 hours
  • Television for 3 hours
  • Lamp for 4 hours
  • Kettle for 15 minutes
  • Stove for 45 minutes
  • Hairdryer for 15 minutes
  • Determine the average power of each of these items by reading the specifications given on the appliances. Complete the table.
Electrical appliance Power (kW)
Computer
Television
Lamp
Kettle
Stove
Hairdryer

Now complete the following cost assessment:

APPLIANCE POWER (kW) as above TIME Usage(hours) Energy Usage (kW/h) Cost @ R1,50 per hour
Computer
Television
Lamp
Kettle
Stove
Hairdryer

QUESTIONS

1. What is your deduction?

2. Are you aware of the need to use energy more economically? Give your own opinion of this.

3. Calculate the following:

a) A mountaineer whose mass is 75 kg climbs a 320 m rock face in 20 minutes. Calculate his power.

b) A large cupboard weighing 150 kg has to be carried up a stairway approximately 5 m high during a move.

  • How much work is performed?
  • What is the performance rating of the workers if two men are able to do this in 10 minutes?

Assessment of RESEARCH on appliances

Were you able to obtain all the required information and do the calculations?

Could you categorise information?

[LO 1.1; LO 1.2; LO 2.2; LO 2.4]

Assessment

LO 1: Scientific investigations:

The learner will be able to act confidently on curiosity about natural phenomena, and to investigate relationships and solve problems in scientific, technological and environmental contexts.

This is evident when the learner:

  • plans investigations;
  • conducts investigations and collects data.

LO 2: Constructing Science Knowledge:

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

This is evident when the learner:

  • categorises information;
  • interprets information;

2.4 applies knowledge.

Memorandum

Power

Activity

Questions:

Power = Labour (work) Time

Labour = Power (F) × s

Weight = Mass × 10 =  Kg

= F × s Time =

2. a) 1000 Watt, in other words, 1 000 × Joule/second

b) The amount of kW that is delivered or consumed in one hour

3. Larger cars approximately 100 kW; smaller cars approximately 70 kW

4. –

5. Engine has greater power / capacity for doing work

6. First calculate total consumption of energy (kWh):

= kW × h (hour)= 3 kW × 124 h= 372 Kw

Then calculate the costs:

= 372 × R0,35= R130,20

Activity

The power per hour of appliances (more of less):

  • Pocket calculator 0,0006W
  • Microwave oven 750W
  • Drill 500W
  • Radio 28W
  • Toaster 800W
  • Fan 100W
  • Iron 1 200W
  • Stove 1000W
  • Computer 250W

Questions:

1. The greater the power, the higher the cost of using it

2. Debate

3. a) W = F x s= (75 x 10) x 320= 750 x 320= 240 000 J

Power = 240 000 J ( 20 × 60 ) = 240 000 1 200 = 200 W ( or 0,2 lW ) alignl { stack { size 12{ ital "Power"= { { size 11{"240"`"000"`J}} over { size 11{ \( "20" times "60" \) }} } } {} #size 11{ {}= { { size 11{"240"`"000"}} over { size 11{1`"200"}} } } {} # size 11{ {}="200"`W` \( ital "or"`0,2 ital "lW" \) } {}} } {}

b) W = F x s = (150 x 10) x 5= 7 500 J

Drywing = Arbeid Tyd = 7 500 J 600 s = 12 , 5 W alignl { stack { size 12{ size 11{ ital "Drywing"= { { size 11{ ital "Arbeid"}} over { size 11{ ital "Tyd"}} } }} {} #size 11{ {}= { { size 11{7`"500"`J}} over { size 11{"600"`s}} } } {} # size 11{ {}="12",5`W} {}} } {}

 One worker's performance = 12,5  2= 6,25 W

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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Source:  OpenStax, Natural sciences grade 9. OpenStax CNX. Sep 15, 2009 Download for free at http://cnx.org/content/col11069/1.1
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